1. Field of the Invention
The present invention relates to a composition for solubilizing a hardly water-soluble medical agent, as well as a pre-concentrate for solubilizing a hardly water-soluble compound, which contains the composition and the compound.
2. Description of the Related Art
A hardly water-soluble medical agent has a problem that intestinal absorbability and bioavailability are low owing to its low solubility in water. Moreover, also in the development of new drugs, there frequently arises an extremely serious problem in the case where the drugs are hardly water-soluble. Particularly, since most of new-drug candidate substances for antimalignant tumor drugs, immunosuppressive agents, antibiotics, antifungal agents, antihyperlipidemic agents, antiinflammatory agents, and the like are hardly water-soluble and cannot be solubilized, various tests such as toxicity tests cannot be performed and thus the substances frequently become pending or drop out during their development even when they have a sufficient pharmacological activity.
Thus, hitherto, as formulation of a hardly water-soluble medical agent, there has been investigated solubilization using a thermodynamically stable microemulsion.
However, for microemulsification, a high-pressure emulsifier is frequently used in order to reduce particle size and there is a problem that activity may decrease depending on a medical agent under the influence of friction heat at high-pressure emulsification. Moreover, even when oil drops themselves in the microemulsion are stable (small particle size), by the crystal growth of the hardly water-soluble medical agent during storage, the medical agent may be frequently precipitated. In addition, since most of the composition in microemulsion is water, the microemulsion cannot be encapsulated (gelatin to be used as a capsule film is dissolved), so that the drug form is basically limited to a liquid. Therefore, there are problems in view of compliance, for example, bitter taste originated from the medical agent and increased dosage per one dose.
For example, in WO03/066025A1, transparent aqueous gel and aqueous solution of β-carotene have been prepared using a polyol, an ester of an unsaturated fatty acid, a surfactant, and water. As a specific example, an aqueous gel containing β-carotene has been prepared using ethyl linoleate, polysorbate 80, glycerin, lecithin, water, and the like. The composition is different from the pre-concentrate in the invention in the facts that ethyl linoleate is substantially used as an unsaturated fatty acid ester and lecithin (main ingredient: phosphatidylcholine) is used as an additional component in addition to the fact that water is contained.
Since the composition is a preparation containing water in a high ratio, a gelatin capsule cannot be applied and, particularly in the case of an aqueous solution, there is a problem of stability as a preparation, e.g., increase in particle size with the passage of time through occurrence of aggregation and integration of particles. Moreover, a highly crystalline hardly water-soluble medical agent cannot be dissolved in the composition in a high concentration. Furthermore, the composition is a formulation or a preparation method limited to β-carotene and, since heating at 160 to 180° C. is necessary at the stage of its preparation, activity of a common hardly water-soluble medical agent considerably decreases.
Moreover, in WO97/36611A1, an oil-in-water type emulsion of cyclosporin is prepared using a middle-chain fatty acid triglyceride, a phospholipid, and water (further using a free fatty acid, glycerin, and a surfactant as additional components). As a specific example, an oil-in-water type emulsion of cyclosporin A is prepared using a middle-chain fatty acid triglyceride (trade name: miglyol 810), linoleic acid, TWEEN 20, glycerin, an egg phospholipid, dimyristoylphosphatidylglycerol (DMPG), and water. The composition is different from the pre-concentrate in the invention in the facts that linoleic acid which is a free fatty acid is used as an additional component and the egg phospholipid (main ingredient: phosphatidylcholine) is contained as a phospholipid component in addition to the fact that water is contained.
Furthermore, in U.S. Pat. No. 5,658,898, a nanoemulsion of staurosporin derivative is prepared using a triglyceride, a phospholipid, a partial fatty acid ester of polyoxyethylene sorbitan, and water. As a specific example, a nanoemulsion is prepared using a middle-chain fatty acid triglyceride (trade name: miglyol 812), polysorbate 80, lecithin derived from soybean oil (trade name: LIPOID S 100), and water. The composition is different from the pre-concentrate in the invention in the facts that a polyhydric alcohol is not contained and lecithin derived from soybean oil (main ingredient: phosphatidylcholine) is used as a phospholipid in addition to the fact that water is contained.
With regard to the compositions described in WO03/066025A1, WO97/36611A1, and U.S. Pat. No. 5,658,898, emulsification by a high-pressure emulsifier is required for preparing an objective emulsion, and the compositions are deactivated under the influence of high-pressure emulsification depending on a medical agent. Moreover, since the ratio of an aqueous phase is high, direct gelatin encapsulation is impossible. However, a pre-concentrate with a component other than water does not have self-emulsifying ability (self-micro- or nano-emulsifying ability) and its drug form for oral administration is limited to a liquid. In the case where the drug form of the hardly water-soluble medical agent is a liquid (emulsion), aggregation and integration of particles occur and particle size increases with the passage of time, so that stability as a preparation cannot be said to be sufficient.
Based on these backgrounds, recently, as a preparation of a hardly water-soluble medical agent, there has been developed a self-emulsification (self-microemulsification) type drug delivery system (SMEDDS; also called as microemulsion pre-concentrate (MEPC)) wherein the preparation itself does not contain water and is easily dispersed or dissolved in water. However, there has been hitherto not known a solubilizing composition which satisfies all requirements, demanded as performance of the SMEDDS preparation, that it is stable as a pre-concentrate, a medical agent can be contained in a high concentration, self-emulsification (self-microemulsification) is possible, a dispersion rate into water is high, particle size after solubilization is small, and intestinal absorbability is high and which is applicable to various hardly water-soluble medical agents.
3. Problems to be Solved by the Invention
An object of the invention is to provide a solubilizing composition which satisfies all requirements demanded for the aforementioned SMEDDS preparation and also is widely applicable to various hardly water-soluble medical agents, to prepare a solubilizing pre-concentrate of a hardly water-soluble medical agent using the composition, and, as a result, to improve bioavailability of the hardly water-soluble medical agent.